At various points during manufacturing (e.g. before or after texturing) of a workpiece, it is desirable to inspect a workpiece for bumps, pits, contaminant particles, or other defects. Conventional optical inspection systems rotate a workpiece with a single encoder spindle system to move the workpiece relative to laser beams that scan the workpiece for defects. A single encoder in some conventional optical inspection systems may be designed for high speed scanning, but has a low resolution. For example, one optical inspection system manufactured by KLA-Tencor uses a single encoder with high scanning speed, but with a low resolution of 0.25 degrees. Other conventional optical inspection systems are designed with a single encoder that has a high resolution but low scanning speed, for example, KLA-Tencor's Candela Optical Surface Analyzer (OSA).
Using such single encoder spindle systems requires a tradeoff between a static high resolution angular positioning capability and a maximum rotational speed due to the bandwidth limitation of the encoder signals.